SOIL CHEMISTRY: E. W. HILGARD 
9 
The material, looking like an ordinary dark gray clay, adhered strongly 
to the tongue, and with a Httle water became very plastic. Unfortu- 
nately the main sample collected by Dr. Shaw came to the laboratory 
unlabeled and was by mistake thrown away by an assistant. A small 
sample of about 24 grams, however, was left; and on this the entire in- 
vestigation had to be made. About half of this sample was boiled in 
distilled water for 24 hours for sedimentation, as there were some coarse 
particles, apparently of talcose schist. A reference to geological descrip- 
tions of the basin of Mexico, in which serpentines and talcose rocks are 
prevalent, seemed to confirm this conclusion. 
The suspension did not appear to be very uniform even after pro- 
tracted boiHng, and under the microscope showed a multitude of dark 
rounded particles, very uniformly distributed through a colloidal medium 
of faintly yellowish tint, which when colored with a solution of ^malachite 
green' merely showed the fine discrete particles in larger numbers and 
greater fineness. 
All attempts to free the colloidal ingredients from the visibly discrete 
particles by sedimentation proved futile. The suspension was readily 
coagulated and precipitated, apparently unchanged, by a solution of 
sodium chloride. On washing by decantation the suspension was again 
readily made, the microscopic character also remaining the same. 
As the original material effervesced somewhat with hydrochloric acid 
it was conjectured that the minute grains might be earth carbonates; 
but the addition of drops of tenth-normal acid was slow in producing 
coagulation, doubtless on account of the neutralization of the acid by 
the earth carbonates. The filtrate gave reactions of calcium and more 
strongly of magnesium; yet the coagulum itself seemed to contain as 
many discrete particles as before, showing that the earth carbonates 
were very finely distributed, and not visible. 
For the determination of the specific gravity some pure selected frag- 
ments weighing 1 .073 grams were dried in a 25 cc. bottle. Filling the bot- 
tle, 0.481 gram of water was found to have been displaced, making the spe- 
cific gravity about 2.25, nearly that of kaohnite clays. The substance 
was left in the gravity bottle until, with the aid of slight heating, it had 
absorbed the maximum amount of water, leaving a clear remainder 
above it. The water poured off measured 14 cc, showing that 11 cc. had 
been taken up by the clay, forming a coherent, gelatinous-looking mass, 
and giving an increase of bulk equal to about 25 times the volume of the 
clay. The mass was then evaporated to dryness in an air bath, with 
suction, at about 50°C., in order to avoid a possible molecular change; 
the bottle then was refilled with water. The reabsorption took place 
